Gaudete (Rejoice) is the name given to a series of verses published as part of the 1582 Finnish collection of mediaeval devotional music Piae Cantiones ecclesiasticae et scholasticae veterum episcoporum (Devout ecclesiastical and scholastic songs of the venerable bishops) which contains 74 songs sung at Finnish Cathedral schools.
The verses have no title in the Piae Cantiones, and are thought to have derived from Bohemian song Ezechielis porta (referring to the portal described in Ezekiel 44:2 )with a refrain added by the editor of the collection, Jaakko Finne, rector of the Turku Cathedral School.
The carol, like many Latin anthem, fell largely into disuse throughout the 19th and 20th century, but was given a new lease of life in 1972 when folk rock group Steeleye Span sang it a capella it on their Below the Salt album – reaching No 14 in the chart, it became the band's first hit.. The tune used in this version is said to differ from the original significantly in the verse portions (possibly to give Maddy Prior's voice a decent chance to soar) but is pretty much identical in the semi-chanted refrain. Since then, it has been sung along to radios and by carolers, although it remains rare in churches.
The English translation below is my own version.
Refrain
Gaudete, gaudete! Christus est natus
Ex Maria virgine, gaudete!
Rejoice, rejoice! Christ is born
of Mary, the Virgin, rejoice!
Tempus adest gratiae
Hoc quod optibamus,
Carmina laetitiae
Devote redamus.
The time of grace we have
awaited is upon us,
let us offer up, with devotion
our songs of joyful praise.
Deus homo factus est
Natura mirante,
Mundus renovatus est
A Christo regnante.
God is made man and
all nature marvels at
the world made new
through Christ the King.
Ezechielis porta
Clausa pertransitur,
Unde lux est orta
Salus invenitur.
Ezekiel's death-bound gateway
gives way to
the rising light.
Salvation passes through.
Ergo nostra cantio,
Psallat iam in lustro;
Benedicat Domino:
Salus Regi nostro.
So, let us sing, together,
loudly, lustily.
Let us bless God,
our king and saviour
Sources:
http://www.hymnsandcarolsofchristmas.com/Hymns_and_Carols/Biographies/piae_cantiones.htm
http://steeleye.freeservers.com/gaudete.htm